INCREASE AND LIMITS OF GROWTH YIELDS FOR HETEROTROPHIC MICROORGANISMS

Substrates for heterotrophic growth of microorganisms are more or less energy-limited. In order to improve the growth yields phenotypic and genetic measures come into consideration. By means of the auxiliary substrate concept the carbon metabolism determined carbon conversion efficiency of about 75% for C2 compounds (i.e. non-glycolytic, gluconeogenetic substrates) and about 85%, respectively, for C3 or glycolytic substrates can be attained experimentally. With methylotrophic microorganisms the growth yield might approach to this limit if the methanol oxidizing methanol dehydrogenase (bacteria) and methanol oxidase (yeasts) are replaced by an NAD+-linked dehydrogenase. Due to an increase in the overall P/O quotient up to the maximum this limit cannot be reached.